Throttle body question

[havin-fun]

On the lower front side of the throttle body there is a 1/2 inch open (looks like a hose fitting) nipple is this suppose to be open or capped, what is it for.

 

[truckins10]

The 5.7liters used this passage to help heat the throttle body by running hot coolent through there. Our application does not use them. Fern